Miniaturization of semiconductor devices and so on has the advantage of achieving improvement in performance and function (high-speed operation, low power consumption, etc.) and reduction in cost and is increasingly accelerated. Such miniaturization is supported by the lithography technology. A transfer mask is one of key techniques, as well as an exposure apparatus and a resist material.
In recent years, development is made of the technology for a 45 nm to 32 nm half-pitch (hp) generation defined in the semiconductor design rule. The half pitch of 45 nm to 32 nm corresponds to ¼ to ⅙ of the wavelength of 193 nm of ArF excimer laser exposure light (hereinafter referred to as “ArF exposure light”). In particular, in the 45 nm hp generation and beyond, only the application of the resolution enhancement technology (RET) such as conventional phase shift technique, oblique-incidence illumination, and pupil filtering, and the optical proximity correction (OPC) has become insufficient. Therefore, the hyper-NA technique (immersion lithography) and the double exposure (double patterning) technique are required.
In the meantime, circuit patterns necessary in the semiconductor manufacture are exposed in sequence onto a semiconductor wafer by a plurality of photomask (reticle) patterns. For example, a reduced projection exposure apparatus with a predetermined reticle set therein repeatedly projects and exposes patterns while sequentially shifting projection regions on a semiconductor wafer (step-and-repeat system), or repeatedly projects and exposes patterns while synchronously scanning the reticle and a semiconductor wafer with respect to a projection optical system (step-and-scan system). By this, a predetermined number of integrated circuit chip regions are formed in the semiconductor wafer.
A photomask (reticle) has a region formed with a transfer pattern and a peripheral region thereof, i.e. an edge region along four sides in the photomask (reticle). When exposing the transfer pattern of the photomask (reticle) while sequentially shifting projection regions on a semiconductor wafer, the transfer pattern is exposed and transferred onto the projection regions so that the photomask peripheral regions overlap each other for the purpose of increasing the number of integrated circuit chips to be formed. In order to prevent exposure of a resist on the wafer due to such overlapping exposure, a light-shielding band (light-shielder band or light-shielder ring) is formed in the peripheral region of the photomask by mask processing.
The phase shift method is a technique of giving a predetermined phase difference to exposure light transmitted through a phase shift portion, thereby improving the resolution of a transfer pattern using interference of light.
As photomasks improved in resolution by the phase shift method, there are a substrate dug-down type in which a shifter portion is provided by digging down a quartz substrate by etching or the like, and a type in which a shifter portion is provided by patterning a phase shift film formed on a substrate.